1. Field of the Invention
The invention relates to a method and apparatus for making a self-inflatable air mattress or cushion having an adjustable firmness characteristic and the product formed thereby.
2. Description of Related Art
The prior art literature describes several early efforts to make self-inflatable mattresses and the like. For example, U.S. Pat. No. 3,935,690 entitled xe2x80x9cMethod of Packaging and Unpackaging a Self-Inflating Air Mattressxe2x80x9d describes a mattress which can be used for camping and which includes an open cell foam core covered with a air impervious material having a fabric exterior. Such mattresses are satisfactory for certain camping purposes but such mattresses tend to be thin and the edge of such mattresses tend not to be physically attached to the exterior covering material.
U.S. Pat. No. 3,675,377 describes another typical inflatable structure including a flexible foam core portion and a fabric covering.
The problem with structures such as described in U.S. Pat. Nos. 3,675,377 and 3,935,690 is that the exterior material is not bonded to the entire surface of the foam core but, rather, acts like a bag so that when the structure is inflated the sides or edges tend to round out. Accordingly, it is virtually impossible to form a self-inflatable mattress, using prior art techniques, which includes concavities or compound three-dimensional shapes.
FIG. 1A illustrates, in cross-sectional detail, a typical prior art self-inflatable mattress having a core and a covering. Because the coverings tend to be fabric, it is not possible to make a lap seam without losing air as shown in FIGS. 1B and 1C.
If the fabric illustrated in FIGS. 1B and 1C is sealed on only one side, then air tends to escape in the manner indicated. FIG. 1B illustrates a prior art xe2x80x9cfinxe2x80x9d seam and FIG. 1C illustrates a prior art xe2x80x9coverlapxe2x80x9d seam. It is also possible to make an overlap seam, such as illustrated in FIG. 1C, using fabric that is coated on both sides with a cement material between the two layers. Such prior art structures have several major disadvantages. First, and foremost, fabric covers, whether or not wholly or partially sealed on both sides, wrinkle when they turn corners and/or are compressed. Therefore, they cannot adequately conform to irregular shapes and tend to leak. Second, it is not possible to form a satisfactory thermoplastic welded seal between two overlapping layers of single sided coated cloth material, such as illustrated in FIG. 1C. Third, and last, the prior art techniques such as illustrated in FIGS. 1A-1C usually require adhesives or chemicals which are environmentally hazardous.
Other inflatable mattresses or structures are unknown in the prior art. See, for example, U.S. Pat. No. 1,970,803 which describes a method of making an inflatable rubber structure, such as a bed mattress. U.S. Pat. No. 4,991,244 describes an air mattress that includes a means for controlling the density and the relative firmness thereof depending upon the side of the mattress being occupied. Similarly, note U.S. Pat. No. 4,908,895.
Lastly, U.S. Pat. No. 4,167,432 entitled xe2x80x9cProcess of Making a Water Bed Mattressxe2x80x9d describes a technique for forming a bag-like structure that can accept water and act as a suitable bed mattress.
FIG. 1D illustrates a sheet of commercially available dual melt film including a top side S1 having a melt temperature T1 and a bottom surface S2 having a melt temperature T2 which is lower than the melt temperature T1 on the top surface S1. Acceptable films are formed from polyether polyurethane. Such films are generally used for purposes other than making self-inflating air mattresses or cushions.
While the prior art does describe a number of efforts to make self-inflating structures, such as mattresses and cushions, nevertheless, when those structures are inflated they tend to have a generally convex shape because the exterior fabric layer does not satisfactorily adhere to the entire foam core. In contrast, Applicant""s invention completely adheres to the surface of the foam core thereby permitting larger structures, having a defined shape, and which includes concave and compound portions, flat sides and right angle edges.
Briefly described, the invention comprises a method and apparatus for making self-inflatable mattresses and cushions having an open pore foam core and an exterior surface formed from dual melt films. Initially, a core block of open pore foam material is placed on a flat surface or conveyer belt and a top sheet comprising a layer of dual melt film is placed on top thereof so that the edges of the film drape over the sides of the core. A non-stick, heat transfer, buffer layer is then placed on top of the film so that the top layer of the film does not adhere to the heating agent which could comprise a conventional heating iron or a heat and pressure roller. The film has a top surface S1 having a first melt temperature T1 and a bottom surface S2 having a melt temperature T2 which is lower than the melt temperature T1 of the top surface S1. Heat TR and pressure, preferably from a roller, are then applied to the top sheet. The heat of TR is such that the bottom layer S2 of the dual melt film melts and adheres to the foam core but the top layer S1 does not melt. A pair of heated pressure rollers apply heat, through another buffer layer, to the side portions of the top layer that overlap the edge of the foam core so that the entire top sheet adheres to the foam core leaving only small corner tails to be folded in later and sealed. The foam core is then turned over and a bottom layer of dual melt film is placed on top of it so that its sides drape over the edges of the block and heat and pressure are again applied, through a buffer layer, preferably with a roller, to cause the bottom layer to adhere to the bottom of the foam core. The same pair of side pressure rollers causes the edges that drape over the foam core to adhere to the sides of the core and to the top layer. The tails, or ears, of both sheets are folded in so that they melt and attach to the block. A valve, which can be either an oral inflation valve or one way valve, is then attached to the side of the mattress. The dual melt film completely encases and contacts the outer surface of the foam core. The mattress can then be squeezed and deflated and kept in that position for easy storage. Subsequently, when it is desired to inflate the mattress, the valve is opened and the mattress naturally assumes its original shape. Because the dual melt film completely encases the entire core, it is possible to form very rigid structures which may include concave indentations or compound three-dimensional forms. Such structures could include, for example, mattresses for beds, seat cushions, back cushions, and special purpose cushions, such as pilot ejection seat cushions.
The invention has several other advantages over the prior art. First, because fabrics are not used, the outer cover does not wrinkle and leak. The dual melt film is relatively soft when applied to the open foam core and conforms to the entire surface thereof. Even though the bottom surface S2 melts, the top surface is relatively soft so that it stretches and conforms to the foam shape whereas cloth is stiff and does not. When the final product is formed, the dual melt film, after it cools, also stretches and moves with the foam core so that it does not wrinkle or pucker and thereby adheres to the basic shape of the foam core when inflated to ambient air temperature or when pressurized Second, the overlapping end seams are bonded by a weld between the bottom surface S2 of one sheet of film and the top surface S1 of the abutting sheet of film. The result is a seal that not only adheres entirely to the edge of the foam core but also adheres to itself in an absolutely airtight fashion. Third, and very importantly, because only heat and pressure is used to laminate the dual melt films together and to the core, the use of adhesives, solvents and hazardous chemicals is avoided.
These and other features of the invention will be more fully understood by reference to the following drawings.